Common hepatic duct

The common hepatic duct (CHD) is formed by the right and left hepatic ducts junction. It joins the cystic duct to form the common bile duct (CBD). It is approximately 4 cm long and 4 mm in diameter, typically. 

Together with the cystic duct (laterally) and cystic artery (superiorly), they form Calot's triangle.

Terminology

It is not always possible to confidently see where the cystic duct enters the common hepatic duct to form the common bile duct on ultrasound imaging. Therefore, some commonly use the term "common duct" as a term conflating the common hepatic and common bile ducts. This is contrary to Gray's Anatomy, which uses the term "common duct" to refer to the duct formed by the confluence of the common bile duct and the pancreatic duct.

Radiographic features

Ultrasound

For decades, what had been labeled "common bile duct" in much radiology literature was, in many cases, actually the common hepatic duct. Thus, the oft-quoted normal value of <6 mm (measured inner aspect of wall to inner aspect of the wall, typically by ultrasound) in adults actually refers to the common hepatic duct in most cases. The common hepatic duct is best measured when the patient is fasting, at the porta hepatis, typically parallel and anterior to the portal vein. 7 mm has since been proposed as a better cut-off.

Also, for decades, it had been thought that the common hepatic duct (often erroneously termed the common bile duct) could increase as much as 4 mm after cholecystectomy and by age by as much as 1 mm per decade after 60 years of age. This has not been supported by subsequent studies, which indicate that the common hepatic duct diameter may increase only by 0.1-0.2 mm per decade and increases only about 1 mm after cholecystectomy.

The diameter of the actual common bile duct is far more variable, not readily affording a valid cut-off value. It is seen more inferiorly by ultrasound, usually having exited the porta toward the pancreas.